The blades and vanes of gas turbine machines operate in an extremely harsh environment with high gas pressures and velocities and temperatures around 1300° C. In order to withstand this environment, the blades and vanes in a combustion turbine are made of high temperature alloys such as nickel-cobalt, are coated with a thermal barrier coating (TBC) such as yttria-zirconia, and, if necessary, are internally cooled to help dissipate heat. The condition of the TBC is critical because spalling, where areas of the TBC peel or flake away from a vane or blade, can lead to vane or blade failure within hours. At present, machines are shut down at regular intervals and inspected, and damaged blades and vanes are then replaced. Condition monitoring of vanes and blades of operating machines until now has not been available, although gas monitoring has been proposed to look for particulates from the thermal barrier coating as an early warning system.
Typically, gas turbine machines have three or four rows of vanes and blades having a TBC and which are subjected to the most severe conditions. There may be, depending upon the type of machine, about 50 to 100 blades and vanes per row, and up to approximately 200-500 total blades and vanes having a TBC. Currently, it is necessary to periodically stop the turbine and inspect all of these components for deterioration of the coating or other defects. It would be desirable to determine the condition of the thermal barrier coating of these components while a gas turbine machine is in operation. Avoiding the need to periodically stop the turbine for inspection reduces downtime and increases turbine efficiency. Similarly, early detection of defects reduces repair costs and outage time, again increasing turbine efficiency. A need exists for monitoring the condition of the thermal barrier coating of blades and vanes within the turbine over time, while the turbine is in operation, to detect changes in the coating and deterioration thereof.
Various methods and systems for detecting and locating defects within a turbine engine or in turbine components have been proposed. For example, various pending applications of the current inventors cover methods of acoustic waveguide or radio frequency monitoring of turbines to detect deterioration in the coating or the presence of foreign objects in the turbine.
However, there is a continued need for new methods and apparatus for detecting the deterioration of the thermal barrier coating on blades and vanes in a combustion turbine, to provide an indication of when a turbine needs to be shut down for maintenance.